This laser star is fully operational

Laser-guided adaptive optics are all the rage for telescopes nowadays. A laser guide star helps the software that processes telescope data figure out how to compensate for the shimmer of Earth’s atmosphere. And besides, it can make for a cool “Star Wars” special effect, as seen in this composite image of the European Southern Observatory’s Very Large Telescope in Chile.

ESO astronomer Yuri Beletsky set up the picture while his colleagues were pointing the guide-star system at the dense core of our own Milky Way galaxy, hanging in the clear skies above Chile's Atacama Desert. The Very Large Telescope is actually four separate telescope units, working together in an array. This particular unit is named Yepun, which is the word for the star Sirius in the language of the region's indigenous people.

Yepun's laser guide system energizes sodium atoms at an altitude of 56 miles (90 kilometers). The telescope system's software uses that artificial "star" to determine how light is blurred as it shines down through the atmosphere. Those readings can in turn be factored into astronomical observations, to add sharpness to what otherwise would be blurry images. This is the process that's known as adaptive optics, and it's being used more and more to produce images from ground-based telescopes that can rival the Hubble Space Telescope's sharpest stunners.

In an e-mail, Beletsky explains how he blended two frames to create the picture you see here.

"The image was taken with a Canon 5D Mark II camera + Canon 15/2.8 Fisheye lens. The image is actually a mosaic of two frames, where each one was taken with 30-second exposure. Due to the very small focal length (15 mm) the stars are not trailed (because of Earth's rotation — the longer the focal length, the shorter should the exposure in order to avoid trailing). Then those images were carefully aligned in data reduction software.

"Now, regarding the colors. At night, human eyes are not sensitive to colors. Therefore, in reality, the Milky Way looks colorless (while on the image it does have a color). In contrast, the laser beam is bright enough to see its color with our eyes. The only issue is that on the image the laser beam looks really bright (due to long exposure time), while in reality it has a very deep and dim orange color."